A225375 Odd numbers with exactly 2 distinct prime factors.

15, 21, 33, 35, 39, 45, 51, 55, 57, 63, 65, 69, 75, 77, 85, 87, 91, 93, 95, 99, 111, 115, 117, 119, 123, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 171, 175, 177, 183, 185, 187, 189, 201, 203, 205, 207, 209, 213, 215, 217, 219, 221, 225, 235, 237

Offset

1,1

Comments

Numbers of the form p^i*q^j where p, q are distinct odd primes and i>=1, j>=1.

Subset of A098905 (which contains in addition A046390 and numbers like 255255, 285285, 345345, 373065 etc.).

Links

Table of n, a(n) for n=1..56.

Maple

isA225375 := proc(n) RETURN( (n mod 2 = 1) and (A001221(n) = 2) ); end proc:
for n from 1 to 840 do if isA225375(n) then printf("%d, ", n) ; end if; end do:

Mathematica

Select[2 Range[200] + 1, PrimeNu[#] == 2&] (* Jean-François Alcover, Apr 04 2020 *)

Prog

(PARI) is_A046388(n)={ bittest(n, 0) & omega(n)==2 } \\ M. F. Hasler, Feb 13 2012

Crossrefs

Subsequence of A272592. A046388 is a subsequence.

Cf. A046315, A046390, A046404, A024556, A056913.

Different from A046388, A098905.

Sequence in context: A185307 A061346 A098905 * A329229 A146166 A024556

Adjacent sequences: A225372 A225373 A225374 * A225376 A225377 A225378

Keyword

nonn

Author

R. J. Mathar, Oct 13 2008

Extensions

Entry created by N. J. A. Sloane, May 09 2013 in order to restore the original definition of A046388.

Status

approved